NEW AIRBAG SPREADS OUT BEFORE INFLATING

DETROIT - Many automakers are promoting less powerful airbags to cut deaths caused by the safety restraint.

But Autoliv North America Inc. has unveiled a new airbag that inflates with full force, yet is less liable to cause injury.

The key to the new airbag, which Autoliv calls the Umbrella Radial Deployment System, is an inner layer.

This forces the bag to spread out to its full diameter before inflating outward toward the driver.

A conventional airbag first fires outward toward the driver before unfolding and inflating into a pillow shape.

US safety standards require the airbag to protect an unbelted, average-sized male in a 50kph frontal crash, so the bag must deploy at about 320kph.

More than 1,800 lives have been saved by airbags in the past 11 years, estimates the National Highway Traffic Safety Administration. But the agency has also recorded 61 deaths due to airbag deployments. Of them, 38 were children who were unbelted or riding in car seats in front of a passenger-side airbag.

In March, the US NHTSA amended its rules to let automakers use depowered airbags.

Those bags use a smaller inflator charge so they open slower and with less force. Depowered airbags will not offer as much protection to unbelted adults.

Autoliv has proved to the NHTSA that its technology works and has shown it to automakers, who are interested, said Patrick Jarboe, director of advanced engineering. But Autoliv does not yet have any signed production contracts, an Autoliv spokesman said.

Two advantages

It is unlikely the new airbag could be in use before the 1999 model year, Jarboe said. He said the new airbag offers two main advantages:

It uses a full-powered inflator, yet the deployment strategy makes it comparable to a depowered airbag in terms of its impact upon a human body. The new airbag design also works with depowered inflators, Jarboe said

The airbag is less harmful to out-of-position drivers, particularly if the driver's head is close to the steering wheel. Standard airbags tend to deploy underneath the driver's chin. The force of the deployment throws the driver's head back, often causing head and neck injuries.

Autoliv's new airbag slides up between the driver's head and the steering wheel before inflating, so it does not get trapped under the chin, Jarboe said.

Depowered airbags fill the under-chin space slower, Jarboe said, but still have the same problem as conventional airbags.

Search for gentle airbags

The new airbag was developed in nine months, Jarboe said, as part of a companywide effort within Sweden-based Autoliv GmbH to create gentle airbags.

Engineers at Autoliv's facilities in the US and Europe tried several unsuccessful methods, such as folding the bag differently to change the manner in which it deployed.

The solution was found in the way Autoliv makes some of its airbags - weaving them on a loom at its Airbags International Ltd. subsidiary in Congleton, UK.

Conventional airbags have only two layers of fabric. Autoliv engineers added a third, inner layer to the bag. The inner layer is woven in a specific pattern to the back side of the airbag and contains vents to the outer layer.

When the airbag deploys, the inner layer forces the inflation gas to spread the airbag out first. Then the gas passes through the ports and fills the larger, outer chamber of the airbag to create the cushion.

Adding the extra layer of fabric makes the folded airbag bigger, Jarboe said. Some steering wheels would have to be re-engineered to accept the Autoliv airbag.

The additional cost for the new airbag itself is minimal, a company spokesman said. Automakers today spend about $70-$80 for a driver-side airbag and $80-$90 for a passenger-side airbag, the spokesman said.

Autoliv is also working to adapt the technology to passenger-side airbags and hopes to be able to announce a production-ready system in two to three months, Jarboe said. Passenger-side airbags pose more challenges because some deploy through the top of the instrument panel and others fire through the front.